The 2002 Moscow theater attack shows gas-based raids are not any less dangerous
I think the intent here was to have the fentanyl put the assailants to sleep. Granted, it went horribly wrong. But violent isn't how I would describe the intent.
The FBI tried that once upon a time in Texas. Most formulations of tear "gas" are actually a powder that happens to be flammable powder. It makes nasty poisonous things when it burns (burning already poisonous things has a tendency of doing that). It didn't go well.[1] It's generally not prudent to use tear gas if you're not ok with substantially increasing the likelihood of many people in the target area dying. What's acceptable when you're trying to gas some enemy combatants out of a tunnel in a war zone is not necessarily acceptable for a civilian law enforcement agency to do domestically.
(possibly NSFW) https://www.documentingreality.com/forum/attachments/f240/14...
That said, there are a lot of different gas varieties, and I've only been exposed to that one.
As far as I know this is also a factor why chemical weapons weren’t used in WW2. They are way too hard to control to be useful.
It was pretty damn shitty that the Russian government did little to assist doctors treating hostages in the aftermath, but aside from that their gas plan worked pretty damn well, considering the circumstance they were up against. The only other realistic option was for the Russian government to give in to the demands, as they did years before during the lesser known but larger Budyonnovsk hospital attack after conventional attacks failed (over the course of which something like 150 hostages were killed and hundreds more injured.)